Calvert Jubilee by Wendy Tobitt
In this blog series members of our team share a photo of their favourite spot on our reserves, and tell us the story behind it: what makes it so special, and the work that goes into maintaining it. There’s always more than first meets the eye!
This month, Mark Vallance talks about his lifelong connection with Calvert Jubilee and the landscape around it, and why this reserve is so important for wildlife.
JM: Can you start by telling me what we can see in this photo?
MV: This photo is taken looking out across the reedbed from the hide. This is where I’ve seen really close up views of bittern, going between those channels in the reedbed. It’s a magical place to go and sit and spend an hour just watching nature around you. You can hear Cetti’s warbler from the hide there, which is a fairly rare species with a really loud and distinctive call.
JM: What’s special about Calvert Jubilee for you?
MV: I’ve probably had some of my best wildlife experiences at Calvert Jubilee. I grew up only a mile or so away, so I used to visit as a kid and I remember seeing badgers roaming around the open grassland area at dusk. Since I’ve been at the Trust I’ve had magical views of some really rare bird species on site.
Only about three years ago we had reports of nightingale, which hadn’t been seen for around five years and is really rare in Buckinghamshire these days. I took my mum over to hear it and that pretty much made her year I think, she was over the moon.
We caught a brief glimpse of the bird flying out of the bushes, wonderful. It’s such a magical experience, you can’t hear anything else like it. It makes you feel like you’re in a tropical rainforest. That was a real joy.
One of the key attractions for me is the birds that use the open water. I’ve seen osprey feeding and you get some majestic views of bittern during the winter. That's a skulking kind of bird that spends most of its time in the reedbeds so you get fleeting glimpses generally.
At Calvert Jubilee we manage the reedbed in a certain way with some open channels and the reedbed is really close to the hide. The bittern tend to move between the sections of reedbed and, if you’re patient enough, you can get pretty great views.
I’ve sat in the hide many a time having my lunch while we’ve been out working. One day there were a few of us in the hide and we saw a bittern come out and swim across from one section to another. I’ve never seen that kind of behaviour before. I think we had three bittern overwinter there last year.
Bittern by Tim Stenton
JM: What’s your personal connection with this reserve?
MV: I grew up a mile away from Calvert. I grew up on a farm and as kids we used to spend most of our time out, running up and down hedgerows. I’ve always been really interested in the local landscape around there. I’ve got that deep-rooted connection to the place and the surrounding landscape.
We used to go out on bikes and pop in to Calvert Jubilee, have a nose around looking for devil’s toenails, a fossil found quite often out on the grassy areas. I remember going up with my mum and brother to watch badgers in the evening.
I suppose I lost contact with nature a bit in my teenage years, as many of us do, but then I became a trainee with BBOWT, about 16 or 17 years ago now. We used to travel across Buckinghamshire and Oxfordshire, working on all different sites, but we spent quite a bit of time at Calvert, cutting the reedbed and managing the scrub. I’ve got fond memories of being out with the rest of the trainee team.
I had a brief spell working for the RSPB at Otmoor before coming back to BBOWT as Reserves Officer for Buckinghamshire. Since then I’ve been Reserves Manager and am now Senior Land Manager. I’ve got that whole connection through from my childhood right up to overseeing the management of the site.
JM: Can you tell me more about the history of the site?
MV: Calvert Jubilee has been managed by the Trust since 1976, hence the name Calvert Jubilee - as part of the Queen’s Jubilee celebrations it was designated as a nature reserve and we took control of the management of the site.
It’s an ex-quarry – the lake we see now was Clay Pit Number 2 of the old Calvert Brickworks. Clay Pit No. 2 was fully worked out by 1949, and was formally turned into a nature reserve in 1978. So it’s an ex-industrial landscape which makes it really interesting because nature has recolonised a very manmade landscape.
We talk about rewilding these days, and Calvert Jubilee is a case in point of nature doing its own thing. The importance of many of these ex-industrial brownfield sites is that nature re-establishes itself, and that’s no different than us using the term ‘rewilding’ these days.
In places like College Lake there was a lot of intervention to turn the site into a nature reserve, but at Calvert Jubilee a lot of it happened naturally. We’ve got involved and continued to manage habitat that established itself naturally.
Calvert Jubilee by Jim Asher
Wilding is an interesting thing. I think in the right place it’s definitely the right approach to use to connect back up some of our important wildlife sites, but it’s not the panacea that many people think it is.
We can’t just step back from all of our reserves and let nature take its own route. Management is vital to maintain complex mosaics of habitat and hold back succession, creating and maintaining suitable conditions for many of our rarer species.
If we did nothing then many sites would completely scrub over - ultimately we’d just end up with large swathes of secondary woodland, which would be quite uniform and only be suitable for a small proportion of our native flora and fauna.
JM: Why is this site important for wildlife?
MV: The site is really important for breeding birds in the scrub and reedbed areas. Birds like reed warbler, reed bunting and Cetti’s warbler all breed in areas on or close to the edge of the lake.
The dense scrub provides excellent nesting opportunities for other warbler species such as blackcap and willow warbler, and in the past they’ve also supported breeding populations of nightingale and turtle dove.
Many people know Calvert Jubilee for the birds that create a spectacle on the open water, but it’s also important because of the mix of scrub and open grass, habitats that surround the lake and are home to a vast array of other species.
We have all five of the UK species of hairstreak butterfly on site – it’s one of only a handful of nature reserves in the UK that has that distinction.
Some of the species use the scattered scrub areas out in the grassland and others use the denser scrub thickets and trees, so the mix of habitats is really important.
The five UK species of hairstreak butterfly
JM: How do you manage the site?
MV: We manage Calvert Jubilee for a mix of habitats. It’s a relatively small site but very diverse: open water, reedbed, open grassland, scrub and more mature woodland.
We try to maintain that diversity through our annual management: cutting areas of reedbed and grassland to maintain the openness is critical particularly for some of the rarer butterflies, insects and reptiles. A lot of our work is based on stopping succession – stopping the site from completely scrubbing over, and creating diverse age structures in the scrub and reedbed.
Many of the insect and bird species need a range of age growths to be able to nest in or lay their eggs on. Black and brown hairstreaks solely use blackthorn as their food plant – black hairstreaks lay their eggs on really mature scrub, but brown hairstreaks need young scrub.
It’s the same from a bird point of view, many species will nest in mature trees and scrub, but many of our warbler species need dense thickets to nest in, and some of our rarer species like nightingale will only nest in dense bramble or blackthorn patches. Having that range of age and structure is hugely important.
Much of the landscape around Calvert is quite fragmented, with sites like Calvert Jubilee isolated in areas of intensively managed farmland. Calvert Jubilee sits on the edge of our Bernwood Forest-Upper River Ray Living Landscape, an area which contains a high proportion of sites that are still high in wildlife value.
The fragmented landscape makes Calvert Jubilee reserve much more important. Particularly now, at a time when HS2 is causing so much destruction and damage in the area, our management is much more critical to maintaining and protecting the populations of some of those locally and nationally important species, so that at some point in the future sites like Calvert Jubilee will be able to act as reservoirs to help nature spread back out into the landscape of north Buckinghamshire.
We've got a local volunteer group as well that do a lot of the management at the site who we’re very thankful to, it’s not just us!
Calvert Jubilee by Wendy Tobitt
JM: How does visitor behaviour impact the wildlife on the reserve?
MV: The impact is mainly down to disturbance – many of the rare and threatened bird species nesting on the lake are very easily disturbed by human activity so we try to encourage people to stick to the paths and away from the edge of the lake.
If there’s a high level of disturbance, the adult birds won’t return to their nest so either the eggs will go cold or the young may die on the nest.
We don’t allow dogs on the reserve, as they can be hugely disturbing to ground nesting birds even when on a lead. Some species of bird will nest very close to the paths and could get put off breeding successfully by a dog, even if on a lead, coming by on a regular basis.
We had a problem with antisocial behaviour at Calvert Jubilee during lockdowns, including people swimming in the lake and taking out boats, things that we don’t allow there.
It’s a fragile site and we want to encourage people to behave in a way that’s appropriate to a nature reserve. It’s hugely time consuming for us to try to deal with those issues.
We’re really proud of the fact that we manage such a wonderful site for wildlife and we want to do all we can to protect the species there, and that means encouraging people to enjoy visiting the site while behaving appropriately.
JM: Many of us have heard about Calvert Jubilee mainly because it’s been impacted by HS2. What’s your perspective on that?
MV: It’s hugely disappointing to see a chunk of the nature reserve being cleared for construction purposes for HS2, knowing how important the site is for many of the species mentioned already, particularly the hairstreaks and breeding birds.
Some of the cleared areas are critical for breeding birds. Nightingale and turtle dove both used to nest in the areas they’ve cleared – they haven’t nested there for some years, which is part of a national  decline, but the opportunities for species like that to return are decreased by the loss of habitat due to the creation of HS2.
It’s really disappointing that a site that’s protected as a Local Wildlife Site has no level of protection when it comes to a major infrastructure project like this.
The landscape around Calvert is going to change massively, so it’s not only us losing habitat on the reserve, it’s loss of the farmed environment in the adjacent landscape that many of the species use for feeding, including the hedgerows. The landscape is becoming more fragmented and more barriers are being put in place to stop species from moving, which means that Calvert Jubilee and other sites locally are more vulnerable to issues like increased disturbance from people.
We’ve seen this coming, we’ve done all we can to fight the case, from the Government to the European Court. However, we’re not giving up this fight and will still continue to make our voice heard and make sure wildlife has a place in a landscape cut in two by HS2.
We are still in conversation with HS2 and their contractors about impacts at Calvert Jubilee to ensure that HS2 minimise their impacts on the nature reserve and to make sure that any land that comes back to us is in a state fit for purpose – to make sure it’s being put back to nature in the right way.
Mark Vallance is Senior Reserves Manager for Buckinghamshire.
For more information on getting involved with the Calvert Jubilee volunteer group, contact us.
